Compass locators

[PRB]

Today, while jabber-jawing with an ex-A-6 pilot at work, I learned about these. Apparently, some outer and middle marker beacons have ADF transmitters associated with them, so you can get a needle on your ADF gauge pointing to them. When so equipped, this is called a compass locator. Apparently you would use this feature to help your entry into the line up for the ILS approach. So when I got home from work I got out the AIM-FAR book and read a bit here, and Googled a little there. I figured FS wouldn't have included this in the database, but I was wrong. I found one! The outer marker to Bakersfield (KBPL) runway 30 has an NDB station right on top of it, and with a two-letter ID, which, apparently, distinguishes these ADF stations from the all the other, non-compass locator stations. I got all excited about finding one in FS, so I had to share!

[Milton Shupe]

Wow! Nice range as well. Very helpful especially for those of us who like to navigate with the old steam gauges. :-)

[PRB]

Rgr that Milton. After looking around at the NDB stations in California, I've noticed that almost all the 37 mile stations have two-letter codes, and are co-located at marker beacons, and so are compass locators. That's cool. Apparently these stations typically have short ranges, 15 nm or so, but I think the "weakest" NDB station in FS is 37 nm, right? That would explain why these are the ones used as compass locators.

[olderndirt]

A shame FSX has no provision for ADF reception of the multi-megawatt commercial AM stations.

[Milton Shupe]

Good read: http://en.wikipedia.org/wiki/Non-Directional_Beacon

[robert41]

I use these to line up with runways at many airports.

[mgchrist5]

I've seen a few FSX compass locator beacons in the Northeast US as well, but I never noticed the reception difference between 'regular' NDBs and locators until you mentioned it!


A shame FSX has no provision for ADF reception of the multi-megawatt commercial AM stations.

You can always modify the reception range for VORs/NDBs by using AFCAD. It can be a bit tedious, since I think it can only be done one a one-by-one basis....but it does work. Not sure of the FSX max range potential for NDBs, but VORs I think can only be maxed out to 195nm.

[KellyB]

On the FS9 map for KBGR (Bangor, ME), there apparently was one at the TOTTE outer marker for RWY 33. The latest approach plates and sectionals do not show it, and I'm not sure when it went away.

I used to live at the foot of the hill on which the outer marker was located, and when a plane was on short final, I received a strong steady beep on tv channel 5, which Air Guard pilots thought might be a reflection of the ils signal. It was not BG (_... _ _ .), so it could have been something like that.

So, I'll just backdate myself and ignore present reality, which at my age seems increasingly attractive...:wink:

[PRB]

Good read: http://en.wikipedia.org/wiki/Non-Directional_Beacon
Thanks Milton! Good stuff.


I use these to line up with runways at many airports.
I do as well, but until now I didn't notice that these NDB stations were “co-located” with marker beacons, and that there were part of the ILS system, or that the two-letter ID identified them as “compass locators”.


I used to live at the foot of the hill on which the outer marker was located, and when a plane was on short final, I received a strong steady beep on tv channel 5, which Air Guard pilots thought might be a reflection of the ils signal. It was not BG (_... _ _ .), so it could have been something like that
This raises an interesting point Kelly. If that steady tone on channel 5 was a reflection of the ILS signal, does this mean the ILS only transmits when a plane is actually using it? If so, how does that work?

OT: when I was a wee lad we lived in a house near the end of runway 26 of KAUG in Augusta. Mostly they used 17/35, but occasionally we'd get a show!

[fxsttcb]

A shame FSX has no provision for ADF reception of the multi-megawatt commercial AM stations.
Create 'em! You'll need the SDK installed. Make an NDB, and give it the call letters of your favorite AM Station. Unfortunately the max range of an NDB is 100nm.

Here's the *.xml I used to make CKLW "The Big 8"550

Give it all the proper numerical data, drag it onto BglComp{...\SDK\Environment Kit\BGL Compiler SDK}, and put the *.bgl in an active scenery folder.
You can do the same to create Compass Points using type="COMPASS_POINT"...Don

[Milton Shupe]

Looked at a lot of NDBs in FS9 FSNavigator. Most are 2nm range, but some are 3 and 4. All of the outer marker NDB's I looked at were 2nm ranges.

[Skyhawk_310R]

Most of the time, these are used to combine a directional source with the ability to function as an audible marker for confirmation of overhead status. They are therefore ideal to allow a more low cost option back in the day to let a pilot home in on the marker and confirm when overhead to start the course reversal, which ultimately would line the aircraft up on final approach segment. Back in the day, the need for this was to allow an aircraft to approach the initial approach fix (IAF) from any direction and still have a way to accurately line up on final approach. Having the morse code identifier sound off on the audio panel automatically upon station passage (the marker feature) simply provides a more concrete feedback of being overhead the marker than would be indicated by the classic "needle swing" of passing overhead a traditional NDB station. Think 1930's and this was the state of the art.

Why not just go overhead and turn in to the runway? Well, radius of turn would spit you out wide while a defined procedure turn of some type allowed the accurate line up from any original direction flown to overhead the compass locator. The way to differentiate all this is when you see the "LOM/IAF" title beside a navaid then you know it is a compass locator. BTW: the other name for this is "localizer outer marker." Although there is a third title (just to add to confusion!) calling it a compass outer marker, this title perhaps better captures the dual role of the navaid. The term compass locator goes back to the 1930's when the instrument in the cockpit was itself called a compass locator because it combined bearing function with station passage audio function. Back in that day, you would then perform the course reversal procedure and then use the same compass locator to maintain proper final approach course. For today's ILS or localizer (LOC) instrument approach procedures, the LOM serves simply as the means to navigate to, confirm overhead, and initiate the course reversal at the initial approach fix. After turning on the inbound heading of the course reversal procedure, the pilot then already has tuned the actual localizer and then uses it to turn on and maintain final approach, hence the reason to term it the localizer outer marker (LOM) today.

Of course, in today's world these are fast becoming obsolete as GPS allows navigation to specific waypoints without the need for an external bearing. You just use direct-to-steering to a waypoint that defines the IAF and then fly the route to the final approach fix and go on in. For the older ILS's with an LOM, the pilot merely sets the LOM as a waypoint using standard GPS steering and then likewise the indication of GPS waypont passage to start the published course reversal. This is why modern pilots in aircraft without an ADF tuner can use a certified GPS to fly a full procedure ILS featuring an LOM.

Ken